Created attachment 1717885 [details]
repro.c

syzbot reproducer attached but the issue can be reproduced by just creating the fs and zeroing sb_bsize with gfs2_edit before mounting.

The zero block size causes sd_inptrs to be calculated badly which then causes sd_heightsize to be overrun on initialisation in gfs2_read_sb().

gfs2: fsid=loop0: Trying to join cluster "lock_nolock", "loop0"
gfs2: fsid=loop0: Now mounting FS...
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BUG: KASAN: slab-out-of-bounds in gfs2_read_sb fs/gfs2/ops_fstype.c:342 [inline]
BUG: KASAN: slab-out-of-bounds in init_sb fs/gfs2/ops_fstype.c:479 [inline]
BUG: KASAN: slab-out-of-bounds in gfs2_fill_super+0x1db5/0x3fe0 fs/gfs2/ops_fstype.c:1096
Write of size 8 at addr ffff88809073d548 by task syz-executor940/6853

CPU: 1 PID: 6853 Comm: syz-executor940 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d6/0x29e lib/dump_stack.c:118
 print_address_description+0x66/0x620 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report+0x132/0x1d0 mm/kasan/report.c:530
 gfs2_read_sb fs/gfs2/ops_fstype.c:342 [inline]
 init_sb fs/gfs2/ops_fstype.c:479 [inline]
 gfs2_fill_super+0x1db5/0x3fe0 fs/gfs2/ops_fstype.c:1096
 get_tree_bdev+0x3e9/0x5f0 fs/super.c:1342
 gfs2_get_tree+0x4c/0x1f0 fs/gfs2/ops_fstype.c:1201
 vfs_get_tree+0x88/0x270 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x179d/0x29e0 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x446dba
Code: b8 08 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 fd ad fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 da ad fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007fff4c56e748 EFLAGS: 00000293 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fff4c56e7a0 RCX: 0000000000446dba
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007fff4c56e760
RBP: 00007fff4c56e760 R08: 00007fff4c56e7a0 R09: 00007fff00000015
R10: 0000000002200000 R11: 0000000000000293 R12: 0000000000000001
R13: 0000000000000004 R14: 0000000000000003 R15: 0000000000000003

Allocated by task 6853:
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc+0x100/0x130 mm/kasan/common.c:461
 kmem_cache_alloc_trace+0x1e4/0x2e0 mm/slab.c:3554
 kmalloc include/linux/slab.h:554 [inline]
 kzalloc include/linux/slab.h:666 [inline]
 init_sbd fs/gfs2/ops_fstype.c:77 [inline]
 gfs2_fill_super+0xb6/0x3fe0 fs/gfs2/ops_fstype.c:1018
 get_tree_bdev+0x3e9/0x5f0 fs/super.c:1342
 gfs2_get_tree+0x4c/0x1f0 fs/gfs2/ops_fstype.c:1201
 vfs_get_tree+0x88/0x270 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x179d/0x29e0 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff88809073c000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 5448 bytes inside of
 8192-byte region [ffff88809073c000, ffff88809073e000)
The buggy address belongs to the page:
page:00000000bd4b0b2d refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x9073c
head:00000000bd4b0b2d order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea00028e5608 ffff8880aa441b50 ffff8880aa440a00
raw: 0000000000000000 ffff88809073c000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809073d400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88809073d480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88809073d500: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
                                              ^
 ffff88809073d580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809073d600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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